This invention relates to a process of recovering lactose from milk whey or cheese whey with a good yield. The process according to the invention is characterized by the steps of concentrating whey, crystallizing part of the lactose, and separating and drying the crystals; purifying the mother liquor by separating calcium, fat and proteins, fractionating the purified mother liquor chromatographically, eluting with water, and recovering the following fractions: protein fraction, also containing salts, intermediate fraction which is recirculated to the fractionating step, and a lactose fraction which is passed to the crystallizing step, and possibly a dilute lactose fraction which is recirculated to the fractionating step.
Milk whey is the most important raw-material source of lactose. Lactose can be crystallized directly from whey, in which case the yield, however, is rather poor and the degree of purity of the lactose is low. Various processes have been developed for improving the yield and quality of lactose; these are
summarized in Milchwissenschaft 1986, p. 700-703 and 774-779.
In general, the object has been to provide a process in which both the proteins and lactose contained in whey are recovered. A problem has been that in the crystallization a major part of the lactose remains in the mother liquor, from which lactose is difficult to recover. Mother liquor is thus a waste product without any significant use.
British Patent Specification No. 1,430,490 discloses a process for chromatographically separating whey. The process utilizes a cation exchange resin in calcium form and three fractions are recovered: a protein fraction, lactose fraction and calcium lactate fraction. An intermediate fraction can be taken from between the lactose fraction and the calcium lactate fraction and recirculated.
However, the recovery of pure lactose by this prior process is difficult, because the lactose fraction is positioned between and partly under the other two fractions. In addition, the amount of liquid to be treated is large, which makes the process difficult to carry out.
Particularly problematic are wheys containing relatively plenty of calcium, such as whey obtained in the production of Edam cheese. In the separation of whey, calcium concentrates in the mother liquor, the calcium content of which rises even up to 0.5%. Such a high calcium content together with a low pH causes precipitation in the chromatographic separation columns, thus resulting in a greater need of regeneration. Since the pH of the solution typically drops during the chromatographic separation, conditions in the column become such that certain proteins (such as lactalbumin and lactoglobulin) are also precipitated.